Flotation of carbonaceous ores



Patented Sept. 20, 1938 PATENT OFFICE FLOTATION or CARBONACEOUS omis Charles H. Breerwood, Narberth, P-a., assignor to Separation Process Company, a corporation of Delaware No Drawing. Application September 10, 1937, Serial No. 163,302

16 Claims.

This invention relates to froth flotation and more particularly to the concentration of the useful or valuable constituent minerals of carbonaceous ores. It has especially to do with the use of lignin sulphonates to depress the carbonaceous matter to permit the selective recovery of the desired minerals by the use of 7 known collecting reagents. It is of general utility in the concentration of both sulphide and oxide 10 ore minerals, including the precious and base metals and the oxide compounds of the alkaline earth metals.

The ores contemplated and which respond successfully to flotation in the present process are which behave similarly to graphite in a flotation pulp. They are commonly referred to in this art as graphitic ores, although the carbonaceous matter, in many of them at least, probably is not true graphite.

Such carbonaceous matter, even in quantities less than 1% of the weight of the ore, inhibits successful concentration of the desired ore mineral or minerals, particularly when at least a. substantial proportion of the latter is present in finely divided forms or slimes. Graphite and the carbon compounds of similar behavior occur in flotation pulps in colloidal or near colloidal sizes. They have natural floatability, and as they have a non-selective coating effect and also cause non-selective natural flocculation, ,the flotation concentrates are contaminated by the fine gangue minerals, and frequently in finely divided oxide ore mineral pulps the grade of the concentrates is little or no better than that of the feed. These compounds have the further disadvantage of absorbing substantial quantities of collecting reagents, particularly the fatty acids. 40 It has been discovered heretofore that the carbonaceous matter can be removed by froth flotation prior to the introduction of the collecting reagents by relying upon the natural floatability of the carbon compounds. This prelimi- 45 nary step of concentration may be carried out in one or more stages in which common frothing agents remove sufiicient quantiLes to permit selective concentration of the desired mineral with known collecting reagents in the later stages. 5 This practice is uneconomical for the recovery those containing graphite, or carbon compounds r the ready floatability of the graphitic carbon,

of precious metals because the natural flocculation caused by the carbonaceous matter involves a prohibitive loss of the fine particles. Even in processes for the recovery of minerals of comparatively little commercial value, the weight 5 losses are uneconomical and in some cases effective concentration cannot be made, as in the treatment of extremely fine grained materials such as some of the blue limestones of the Lehigh Valley district of Pennsylvania. Even where the practice is effective, it will be understood that it requires an increased flotation time and there-fore additional flotation cell capacity as well as the consumption of frothing agents, and, in some cases, an unavoidable excess of frothing agent unbalances the frothing characteristics of one or more of the succeeding stages.

Another important class of carbonaceous ores are those containing silver and gold. Precious metal ores are frequently treated by a combination process of flotation and cyanidation, usually by floating the precious metal minerals and then cyaniding the flotation concentrate. Because of especially in the presence of collecting agents 25 for precious metals, .a large portion of carbon appears in the concentrate. The presence of carbon, in a concentrate which is to be cyanided, is undesirable because carbon acts as a precipitant for precious'metals from their cyanide solutions. This tendency of the precious metals to reprecipitate lowers the 'recoveryin the cyanidation process. i

' It is impractical to float off the carbonaceous material before floating the precious metals, as referred to herein in connection with the flotation of carbonaceous limestone, because of the loss of precious metals if the flotation is sufficiently efiective to remove practically all of the 40 carbon. Unless the carbon is removed completely, the harmful results from the presence of carbon in a concentrate to be cyanided remain because relatively small amounts of carbon will cause serious reprecipitation.

It is accordingly the purpose of the invention to retain but depress the carbonaceous matter and render it completely innocuous, preferably to a degree that satisfactory concentration by reference to both grade and weight recoveries can be made and with normal quantities of the appropriate collecting reagents and frothers, i. e., to render the pulp as amenable to froth flotation as one equivalent in mineral composition but free of carbon.

Ingeneral, the practice of the invention comprises conditioning the flotation pulp at usual water dilutions with a relatively small quantity of a lignin sulphonate, preferably calcium lignin sulphonate. The optimum quantities to be employed are quickly determinable from the ap pearance of the concentrate, the proper balance being obtained when the froth behaves similarly to a carbon free pulp of equivalent composition. A guide to the practical quantities of the depressing reagent will be found in the examples to be given hereinafter to illustrate the application of the process to distinct types of pulps, and which also indicate that excessive quantities of this reagent do not improve the results, and in some cases that excessive quantities are less effective. Further, excessive conditioning time, in some cases at least, decreases the effectiveness in depressing carbonaceous matter.

The depressing reagent is ordinarily added to the pulp prior to the introduction of the collecting reagent, and preferably before the frothing agent is added. Conditioning may be carried out in a conditioner or blunger of conventional type, the reagent being added directly to this apparatus or its feed launder. If the conditioner is provided with an overflow to return excess pulp to storage, the addition of the depressing reagent at this point may involve increasing concentrations beyond an effective limit and will increase the conditioning time, in which case it is preferred to employ additional conditioning apparatus specifically for the purpose, or to add the depressing reagent only to the first flotation cell of the circuit, this cell then serving only as a conditioner. In circuits where the pulp water is recovered and returned to the conditioner, or to the first flotation cell with the feed, the presence of frothing reagent usually causes concentration of the naturally floatable carbonaceous matter and the floccules created by it. These concentrates are, however, quickly destroyed when the depressing reagent is introduced, and substantially no flotation time loss is involved.

Following the step of conditioning, mineral concentration is carried out with the usual quantities of the appropriate collecting and frothing reagents, the operations and their effects being substantially identical to those of a carbon free pulp of similar type. Neither calcium nor sodium "lignin sulphonate appears to modify the action of the common collecting reagents for the precious metals, sulphides, oxides or siliceous minerals. Thus, the xanthates commonly employed for the flotation-of sulphides are unaifected at least in their practical action. In the flotation of oxide ore minerals, the usual fatty acids, such as oleic and flsh oil fatty acids, their mixtures with fuel oil, their soaps and emulsions have been found to react normally. It has also been found that fatty acid and resin acid mixtures or combinations such as talloel, its mixture with mineral oil, and refined saponifled talloel may similarly be employed. The positive ion or cation reagents, eifeitive for concentrating the siliceous components of oxide ore minerals, are those which in solution give a positively charged surface-active ion, and which will be fully described hereinafter, are usually ineiflcient in mineral pulps containing carbon, but react normally and with normal consumption, following the described conditioning step with a lignin sulphonate.

The invention can best be understood by reference to the following examples which illustrate the effectiveness of lignin sulphonates, and particularly calcium lignin sulphonate in depressing the carbon compounds and which will also serve as a guide for the practical application of the process. They cover the principal types of ore minerals, namely a precious metal, with a base metal sulphide in the same ore, and an oxide compound of an alkaline earth metal. The latter also includes a paralleldemonstration of inverted flotation in which the siliceous components are floated by a cation reagent and the oxide ore mineral is recovered as the residue of the flotation operation. The examples accordingly illustrate the use of the invention for recovering one each of the principal mineral types, but it will be realized that the invention is of general utility.

Example No. 1

This example demonstrates the natural floatability" of carbonaceous matter without collecting reagents and the depressing effect of small, increasing quantities of calcium lignin sulphonate. The specimen was pure graphite and the recoveries were as follows:

T tN Conat 'Iailrrt es 0. teen wen wt. wt. lbs'lton 973) 2.20 None 27.82 72.18 0. 50 16.06 83.94 1.0 12. N 87. 20 2. 0

R-l=Calcium lignin sulphonate.

Example No. 2

This example illustrates the practice and utility of the invention in the recovery of both a precious metal, gold, and a base metal sulphide, pyrite, occurring together in a carbonaceous pyritic gold ore. It comprises four groups of twenty-two tests.

Group I includes Tests 6 to 9 inclusive, in which the specimen used was pyritic gold ore, 'containing little or no carbon. Test 6 was a rougher concentration of the natural ore. Tests 7, 8 and 9 were made with the same ore mixed with 8 /2% of pure graphite. Test 7 was equivalent to Test 6, in that the depressor was not used and the poor grade and ratio of concentration are especially to be noted. Test 8 was made after conditioning the pulp with 1 lb. per ton of calciumlignin sulphonate, and is equivalent, particularly in ratio of concentration, to blank Test 6. Test 9 illustrates the eifect of an excess of the depressing reagent, the excess in this case having the effect of depressing pyrite.

Group II includes Tests 10, 11 and 12. The specimen was a natural carbonaceous pyritic gold ore. Test 10 was a blank test i. e., without the depressing reagent. Tests 11 and 12 were made after conditioning respectively with 1 and 2 lbs. of calcium lignin sulphonate. Note the high grade and high ratio of concentration of Test 11 and that the excess of depressor was of no advantage in Test 12.

The specimen was natural carbonaceous gold concentrates. No depressing reagent was used in Tests 13 and 14. The eflect of the calcium lignin sulphonate on the iron recovery is especially to be noted: The natural concentrates used as the specimen assayed Fe-19.2%, insoluble-47.3%. The flotation concentrates assayed: Test 13, Fe-20.5%, insoluble-44.38%; Test 14, Fe- 21.70%, insoluble-39.86%; Test 15, Fe31.40%, insoluble20.66%; Test, 16, Fe-24.6%, insoltibia-31.66%. The cleaned concentrates Test17 assayed Fe36.58%, insoluble 13.08%; Test 18, the cleaned concentrate assayed Fe34.26%, insoluble-15.48%; Test 20, the cleaned concentrate assayed Fe38.50%, insoluble-41.72%.

Group IV includes Tests 21 and 22. The specimen was natural carbonaceous pyritic gold ore and the procedure was the same as Test 11 excepting that the secondary butyl xanthate was staged. Test 22 is included to show that doubling the quantity of copper sul' .Late failed to increase the recovery of gold.

2,180,574 7 Group III includes Tests Nos. 13 to 20 inclusive- This example illustrates the usebf the inven 3 vJ 73 411 1; No. 3

tion for the recovery of a non-metallic oxide ore mineral, calcite irom carbonaceous argillaceous limestone, the objective being to produce concentrates suitable for use in cement manufacture. Each test was made with a separate quantity of X the same specimen. The naturalcrystallizationwas extremely fine, substantially complete mineral bond breakage occurring only in the particle size fraction below 20 microns. The rock assayed 74.2% CaCOa and 0.5% carbon. It was ground to the following fineness for flotation:

Per cent Minus 325 mesh sieve, 44 microns 88.8 Minus 325 mesh sieve, plus 30 microns 6.1 Minus 30 microns, plus; 24 microns 9.3 Minus 24 microns, plus 17 microns 8.8 Minus 17 microns, plus 12.5 microns 13.8 Minus 12.5 microns, plus 10 microns 7.2 Minus 10 microns--. 43.6

The tests are divided into three groups, Group I including Tests 23 to 30 inclusive, Group II in- Assay feed Concentrate Cleaner tail Reagents, lbs/ton Test N 0.

Au Percent Assay Pement Ratio Percent Assay Percent Pine Soda Au recovery of Au recovery R--1 CuSO R-2 R"3 oz/ton weight 02mm Au cont, weight oz/ton Au o1] ash 9o. 97 2. s 0s. 93 1. 1 1 81. 61 2. 600 97. 48 1. 23/1 48. 05 4. 520 92. 46 2. 1/1 67. 76 3. 360 95. 67 1. 5/1 40. 69 5. 260 91. 65 2. 46/1 6. 54 0. 720 44. 4. 920 93. 42 2. 25/1 1 15. 46 0. 580 40. 12 5. 340 90. 57 2. 5/1 13. 18 1. 120 34. 98 5. 460 82. 22 2. 86/1 9. 69 1. 180

The reagents are: R-l calcium lignin sulphonate, R-2 secondary butyl xanthate. R-3 higher alkyl dithiophosphate.

Additional practical flotation details are as follows:

The flotation cell feed of the specimen in Group I was ground to 38% minus 200 mesh sieve. The dilution of the pulp during conditioning and flotation was 22% dry solids, and the flotation time (rougher concentration) was 6 minutes. The specimen used in each of the tests of Group II was ground to 68% minus 200 mesh sieve, and was both conditioned and floated at 22% dry solids and the flotation time of the rougher float was ten minutes. In Group III, the carbonaceous concentrates had a fineness of 92% minus 200 mesh sieve in the feed. The pulp dilution in conditioning and flotation was 22% in Tests 13 and 15, and 11% in Tests 14 and 16, and conditioning dilutions were 43% and flotation dilutions 11% in Tests 17 and 20 inclusive. The flotation time of Tests 15 and 16 was 7 minutes and the remainder 12 minutes. In Group IV these conditions were the same as in Group II. a

The conditioning time for the four groups was 10 minutes.

eluding Tests 31, 32 and 33, and Group III including Tests 34, 35 and 36. In the tests of Group I, a fatty acid, oleic, was used as the collector. In Group II the same frothing and collecting reagents were employed but'in stage oiling, and the concentrates were cleaned by flotation without additional reagents. Group III were inverted flotation tests in which'a positive ion reagent was used to concentrate the siliceous components in the froth. It is to be understood that the "rejects" of this group are to be compared with the concentrates oi the fatty acid flotation tests. Each group contains one test in which the carbon was concentrated by a preliminary step prior to the introduction of the collecting reagent, to show the weight losses and to compare the recoveries with the tests in which a lignin sulphonate was used to depress the carbonaceous matter. The first group includes two blank tests in which the carbon was retained and concentration carried I MW 4 2,190,571. recovery. Group III also includes a blank test utes and a flotation time of 5 minutes, 5565555 for purposes of comparison. the carbon concentration, Test 35, required 1 Reagents, lbs/ton Carbon cone. Cone. Reject 5 TestNo' Sd P t? tP 'tP tP 11 t 5 D H H it. $552,757 5286. 352m 5%. W521. 525%.

27 0.15 1.11 .5 1.9 54. V 0 57 7 s 44 a a 15 Reagents used: minute of conditioning and 4 minutes of flota- R-l Calcium lignin sulphonate. tion, followed by 3 minutes of conditioning and 5 30 F--1 Alcohol frother. minutes of flotation to concentrate the siliceous R-5 Oleic acid. matter, principally mica.

R6 Sodium lignin sulphonate. Tests 2'7, 28 and 29 show that in pulps of some C2 Positive ion reagent. ores, at least, sodium lignin sulphonate is not as The unusual reagents referred to in the foreeffective as calcium lignin sulphonate; Test 27 going table are as follows: demonstrating that a relatively small quantity F-l is a frothing agent comprising a mixof the sodium compound is more satisfactory ture of branched and straight chain aliphatic with relation to weight recovery. Test 29 shows monohydric alcohols boiling between about 152 that the addition of soda ash is sometimes eifec- 40 C..and about 162 C. obtainable along with methtive in combination with this reagent to increase anol by the catalytic hydrogenization of carbon the weight recovery. oxides. It should be understood that an objective in C2 is a reagent of the class discovered by treating such limestones by fatty acid flotation Lenher and described in his co-pending applicaor its equivalent, as in the tests of Group I is to tionSerial No. 730,551, filed June 14, 1934, for raise the grade of the concentrates well above A'flotation reagent. The reagents of this class, 76% 05.00: whereby corrections can be made by 45 effective for the purpose of concentrating silithe addition of iron compounds to combine with ceous components of oxide ore minerals, are those a part of the alumina in the clinkering reaction, which in solution give a positively charged suror to permit correction by the addition of a subface-active ion containing an aliphatic hydrostantially pure silica, such as sandstone, or both. carbon group of at least 8 carbon atoms, prefer- It is a further objective to obtain a relatively high 50 ably quaternary ammonium compounds containweight recovery in view of the cost of grinding ing a hydrocarbon group of from 12 to 18 carbon the rock to such an extreme degree of flneness. atoms wherein the aforesaid constituents in so- As alumina, principally in the form of mica, is lution give a positively charged surface-active the mineral occurring in excessive proportions in ion, preferably the negative ion in solution being this rock, it will be seen that the concentrates of 55 a halogen. Of this class dodecyl amine hydro Tests 23 and 24 are unsatisfactory. The tests 7" chloride is an example. C2" is of this class of Group II are satisfactory because the concenand is, specifically. a mixture of hydrochlorides trates have been cleaned and the alumina conof the higher primary aliphatic amines in which tent lowered, and the high weight recoveries are the alkyl groups correspond in carbon content desirable. In Group 111, Test 36, the micaceous v and composition to the fatty acids occurring namaterial was concentrated and the rejects are turally in coconut oil. The use of these reagents accordingly satisfactory for cement manufacture, for beneflciating cement raw materials is more with the addition of a small quantity of silica. fully described, and claimed, in the co-pending It is an important advantage of the present inapplications of Breerwood and Williams, 4 Serial vention that the prevention of carbonaceous ma- Nos. 163,304 and 163,305, flled September 10, 1937. terial from contaminating flotation concentrate, In the foregoing tests, the conditioning time which forms the subject matter of the invention, for carbon flotation, tests 25 and 31, wasl minute is applicable to carbonaceous ores of such widely and the flotation time was 4 minutes, followed by differing character as argillaceous limestones and further conditioning for5 minutes and a flotation precious metal ores, which are normally consldtime of 4 minutes to concentrate the calcite. In ered to be completely unrelated from a flotation contrast,- for the remaining tests of Groups I and standpoint. This general applicability of the in- II, the conditioning. time was 5 minutes and the vention to such various types of carbonaceous flotation time was 4 minutes. In Group III, Tests ores is one of its important advantages and makes 34 and 36 required a conditioning time of 5 minthe process almost unique in the flotation art,

because practically all flotation processes applicable to precious metal or sulphide ores cannot be used with any degree of success on oxidized ores, particularly those containing compounds of the alkaline earth metals.

I claim:

1. In a method of froth flotation of minerals from carbonaceous ores in the presence of a collecting reagent, a step which comprises adding a lignin sulphonate to depress the carbonaceous matter to a pulp of the ore, and subjecting the pulp to froth flotation in the presence of said lignin sulphonate and in thepresence of the carbonaceous matter.

2. In a method of froth flotation of minerals from carbonaceous ores; a step which comprises conditioning a pulp of the ore with a lignin sulphonate to depress the carbonaceous matter before adding a mineral collecting reagent, and subjecting the pulp to froth flotation in the pres ence of said lignin sulphonate and in the presence of the carbonaceous matter.

3. In a method of froth flotation of minerals from carbonaceous ores in the presence of a collecting reagent, a step which comprises adding calcium lignin sulphonate to a pulp of the ore, and subjecting the pulp to froth flotation in the presence of said lignin sulphonate and in the presence of the carbonaceous matter.

4. In a method of froth flotation of minerals from carbonaceous ores, a step which comprises conditioning a pulp of the ore with calcium lignin "sulphonate before adding a mineral collecting reagent, and subjecting the pulp to froth flotation in the presence of said lignin sulphonate and in the presence of the carbonaceous matter.

In a method of froth flotation of minerals from carbonaceous ores in the presence of a col,- lecting reagent, a step which comprises adding sodium lignin sulphonate to a pulp of the ore, and subjecting thepulp to froth flotation in the presence of said lignin sulphonate and in the presence of the carbonaceous matter.

6. In a method of froth flotation of minerals from carbonaceous ores, a step which comprises conditioning a pulp of the ore with sodium lignin sulphonate before adding a mineral collecting reagent, and subjecting the pulp to froth flotation in the presence of said lignin sulphonate and in the presence of the carbonaceous matter.

'I. In a method of froth flotation of minerals from carbonaceous ores, the steps which comprise conditioning a pulp of carbonaceous flotation concentrates with a lignin sulphonate to depress the carbonaceous matter, and cleaning the conditioned pulp by froth flotation, in the presence of the lignin sulphonate and of the carbonaceous matter.

8. In a method of froth flotation of minerals from carbonaceous ores, the steps which com- Prise conditioning. a pulp of carbonaceous flotation concentrates with calcium lignin sulphonate to depress the carbonaceous matter, and clean; ing the conditioned pulp by froth flotation, in the presence of the calcium'lignin sulphonate and of the carbonaceous matter.

9. In a method of froth flotation of minerals from carbonaceous ores in the presence of a collecting reagent, a step which comprises adding up to about four pounds of calcium lignin sulphoning a collecting reagent, and subjecting the pulp to froth flotation in the presence of the calcium lignin sulphonate, a collecting reagent and the .carbonaceous matter.

11. In a method of froth flotation of precious metal values from carbonaceous ores in the presence of a collecting reagent for the precious metal minerals, the step which comprises adding a quantity of 'a lignin sulphonate to a pulp of the ore to depress the carbonaceous matter, and sub-. jecting the pulp to froth flotation, in the presence of the lignin sulphonate and in the presence of the carbonaceous matter.

12. In a method of froth flotation of precious metal values from carbonaceous ores in the presence of a collecting reagent for the precious metal minerals, the step which comprises adding a quantity of calcium lignin sulphonate to a pulp "of the oreto depress the carbonaceous matter,

and subjecting the pulp to froth flotation, in the presence of the calcium lignin sulphonate and in the presence of the carbonaceous matter.

13. In a method. of froth flotation of gold values from carbonaceous gold ores in the presence of a collecting reagent for the gold minerals, the step which comprises adding a quantity of a lignin sulphonate to a pulp of the ore to depress j the carbonaceous matter, and subjecting the pulp to froth flotation, in the presence of the lignin sulphonate and in the presence of the carbonaceous matter.

14. In a method of froth flotation of gold values from carbonaceous gold ores in the presence of a collecting reagent for the gold minerals, the step which comprises adding a quantity of calcium lignin sulphonate to a pulp of the ore to depress the carbonaceous matter, and subjecting the pulp to froth flotation, in the presence of the calcium lignin sulphonate and the presence of the carbonaceous matter.

15. In a method of froth flotation of gold values from carbonaceous ores, the steps which comprise conditioning a pulp of carbonaceous flotation concentrates containing gold minerals with a quantity of a lignin sulphonate to depress the carbonaceous matter, and cleaning the pulp by froth flotation, in the presence of the lignin I sulphonate and the carbonaceous matter.

16. In a method of froth flotation of gold values from carbonaceous ores, the steps which comprise conditioning a pulp of carbonaceous flotation concentrates containing gold minerals with a quantity of calcium lignin sulphonate to depress the carbonaceous'matter, and cleaning the pulp by froth flotation, in the presence ,of the calcium lignin sulphonate and the carbons-- ceous matter. CHARLES H. BREERWOOD. 

